One Direction singer Zayn Malik, a Muslim born in England, received online death threats for tweeting #FreePalestine, a hashtag that Barbados-born singer Rihanna also tweeted but quickly deleted.

Celebs are using social media accounts, which are essential for building their show business brands, as political platforms that can cause a negative buzz.

Veteran Hollywood publicist Michael Levine cautions clients to be careful about stepping into the public relations controversies that surround any comment on the Israel-Gaza crisis.

Twitter has proven to be a minefield for celebrities.Publicist Michael Levine

"Twitter has proven to be a minefield for celebrities," Levine said Tuesday. "It provides celebrities with an opportunity to make any number of careless mistakes that can come back to haunt them. But in a war environment, where emotions are so high and people are seeing pictures on CNN of babies dying and crying, it's particularly incendiary."

The 140 characters in a Twitter posting are "like you're burping out thoughts," Levine said.

For Malik, it was a hashtag -- #FreePalestine -- the caused an uproar on Sunday. Only 14 characters, it delivered a message of sympathy for residents of Gaza to his 13 million followers that was retweeted more than 200,000 times over the next 24 hours.

The responses ranged from followers saying they were "proud of Zayn" to tweets calling on the singer to "kill himself." Some Israeli fans declared disappointment in the music idol.

Malik hasn't tweeted since, and his publicist declined to comment.

The Twitterverse controversy Rihanna stirred up this summer with messages of support for opponents of the U.S. World Cup team is nothing compared with the reaction to her #FreePalestine tweet on July 15. She deleted it just eight minutes later, but some of her 36 million followers grabbed it first. A source close to the singer explained that it was not an intentional tweet.

Bardem's condemnation of Israel was not a spontaneous or accidental message. The actor sent a 400-word letter to Spanish newspapers last week entitled "Genocide."

In the horror that is happening in Gaza, there is no room for distance or neutrality.Actor Javier Bardem

"In the horror that is happening in Gaza, there is no room for distance or neutrality," Bardem wrote. "It is an occupational war and an extermination one against a town with no means, confined to minimum territory, without water and where hospitals, ambulances and children are targets and alleged terrorists. It is difficult to understand and impossible to justify. And it is embarrassing that the position of the Western international community is allowing such genocide."

Bardem followed it with a similar "open letter" also signed by others, including his wife, Oscar-winning actress Penelope Cruz, and Oscar-winning director Pedro Almodovar.

Cruz sent a statement to CNN on Wednesday defending her participation in the letter:

"I don't want to be misunderstood on this important subject. I'm not an expert on the situation and I'm aware of the complexity of it . My only wish and intention in signing that group letter is the hope that there will be peace in both Israel and Gaza. I am hopeful all parties can agree to a cease fire and there are no more innocent victims on either side of the border. I wish for unity, and peace... I believe in a civilization that can be capable of bringing the courage to have a world where humans can live side by side."

Gal Gadot, the actress cast as the new incarnation of Wonder Woman, used her Facebook page to show support for Israel. Her posting is not a surprise, considering she served in the Israeli army and represented her country as Miss Israel.

...We shall overcome!!! Shabbat Shalom!Actress Gal Gadot

"I am sending my love and prayers to my fellow Israeli citizens," Gadot wrote. "Especially to all the boys and girls who are risking their lives protecting my country against the horrific acts conducted by Hamas, who are hiding like cowards behind women and children...We shall overcome!!! Shabbat Shalom! #weareright #freegazafromhamas #stopterror #coexistance #loveidf"

Israeli model Bar Refaeli quoted Abraham Lincoln in an Instagram post with the hashtag #stopterror: "There is no honorable way to kill, no gentle way to destroy. there is nothing good in war, except its ending"

Dealing w/ Hamas is like dealing w/ a crazy woman who's trying to kill u - u can only hold her wrists so long before you have to slap her

Comedian Bill Maher, whose career is built on controversial commentary, used humor to defend Israel in a tweet: "Dealing w/ Hamas is like dealing w/ a crazy woman who's trying to kill u - u can only hold her wrists so long before you have to slap her"

Sometimes it is silence that speaks. Levine said that some of Hollywood's most prominent Jews, who are "very politically active for liberal causes," have "not said a word of support of Israel" concerning the crisis.